1. Field of the Invention
This invention relates generally to inflatable type modular occupant restraint systems for passenger vehicles or, as they are more commonly known, air bag restraint systems. Such a system may be installed in an automobile or other vehicle, at least in part on the steering wheel for the protection of the driver and also in the dashboard or passenger side instrument panel for passenger protection in the event of a collision. More particularly, this invention relates to an improved horn switch arrangement included in a steering wheel having an air bag restraint system installed therein.
2. Description of Related Art
Horn blowing switch arrangements for steering wheel having inflatable occupant restraint modules are known. Dunford et al., U.S. Pat. No. 3,819,205 discloses a modular occupant restraint system in which an inflator, an inflatable cushion or air bag, and a generally rectangular cover or container for the cushion are all assembled on a support plate which, in turn, is mounted to the steering wheel. Extending from each upper corner of the cover is a portion which is provided with a horn blowing switch of the finger deflectable or pressure actuated push button type. A problem with this arrangement is that when access to the switches for repair or replacement is necessary, the cover must be disassembled from the support plate before the switches are exposed.
Hiramitsu et al., U.S. Pat. No. 5,002,306 discloses an occupant restraint system having a plurality of membrane switches of plane rectangular shape applied to and arranged on the upper surface of the upper wall of a soft synthetic resin pad of a steering wheel, except for a break-open area defined by a thinned breaking portion in H-like shape. The manner of attachment of the switches to the pad is not specified. It is contemplated that the membrane switches may be arranged on the rear surface of the upper wall of the pad. There are several disadvantages with these arrangements. The soft synthetic resin pad is rather deficient in respect to providing a suitable reaction surface for horn switch actuation. Servicing or replacement of the switches necessarily involves exposing internal components of the air bag module assembly, particularly in the case of applying the switches to the rear of the pad, and probably also when the switches are applied to the upper surface thereof because of the probability of damaging the pad when attempting to remove the switches for repair or replacement. Additionally, the arrangement of the lead wires from the membrane switches along side wall portions of the pad to a horn actuating circuit within the vehicle, as illustrated and described, leaves much to be desired in an occupant restraint system that is expected to be operable over the like of the vehicle which may be ten (10) years or more.
Fosnaugh et al., U.S. Pat. No. 4,785,144 discloses a modular occupant restraint system in which a horn blowing switch is actuated when the module cover is depressed. The horn blowing switch includes a support that is mounted within the hub portion of the steering wheel and is provided with a plurality of bolts each of which supports a sleeve member. The bolts thread into the inflatable restraint module. Springs between the support and restraint module space the sleeves from the support. Depression of the module engages the sleeve members with the support to complete the circuit to blow the horn. The horn switch is integral to the steering wheel. However, access to the switch for repair and replacement requires disassembly of the module. Another problem is that the avoidance of the effects of vibration on the module, transmitted from the steering wheel, requires the use of relatively strong springs. This, in turn, requires a relatively strong pressing force on the module in order to operate the horn.